Method of making riveted joint

ABSTRACT

A container wall having a tear portion attached to a tab by a hollow rivet which is formed in the tear strip and which extends through an aperture in the tab. The sheet material around the aperture is deformed outwardly with a liberal radius of curvature to form a boss which terminates in an annular end face forming a conical seat. The end face slopes toward the can top as it extends radially inwardly. The hollow rivet is expanded in a manner to form the head of the rivet against the conical seat to permanently join the tab to the container wall.

U ihilted States Patent 1 91 11 1 Brown et al. 1 Apr. 3, 1973 54 METHOD OF MAKING RIVETED 2,233,820 3 1941 Pavlecka .29 509 JOINT 2,237,338 4 1941 Dale ..29 509 ux 3,326,405 6/1967 Fraze... ..220/54 Inventors: Omar Brown, e ering, Ohio; 3,335,471 5/l968 Dunn ..22o/54 George F. Smyth, Los Angeles, 3,437,229 4/l969 Khoury .....220/54 m: 3,440,713 4 1969 Henchert ..29 509 SSignee: Ermal C. Fraze, yt n, Ohio Primary ExaminerCharlie T. Moon [22] Filed May 10 1971 Attorney-Smyth, Roston & Pavitt [21] Appl. No.: 141,574 [57] ABSTRACT Related Application Data A container wall having a tear portion attached to a tab by a hollow rivet which is formed in the tear strip [62] lggls lionogf Ser. No. 881,408, Dec. 2, 1969, Pat and which extends through an aperture in the tab. The sheet material around the aperture is deformed outwardly with a liberal radius of curvature to form a boss which terminates in an annular end face forming [58] F It! IIIIIIIII 29 5 113pl2l/C a conical seat. The end face slopes toward the can top w 0 can as it extends radially inwardly. The hollow rivet is expanded in a manner to form the head of the rivet against the conical seat to permanently join the tab to [56] References cued the container wall.

UNITED STATES PATENTS 5 Claims, 3 Drawing Figures 2,215,882 9/1940 Maloney ..29/509 UX PATENTEDAPRB ms 3. 724.068

6007a 5 In /A METHOD OF MAKING RIVETED JOINT CROSS-REFERENCES TO RELATED APPLICATIONS This is a division of application Ser. No. 88,408, filed Dec. 2, 1969, now US. Pat. No. 3,637,106.

BACKGROUND OF THE INVENTION The invention relates to a joint between first and second members of sheet material positioned face to face wherein a portion of the first member is formed with an integral hollow rivet that extends through an aperture in the second member. This type of joint is commonly used in an easy opening container wall wherein the hollow rivet is formed in a tear portion and extends through an aperture in a tab that serves as manual means for severing the tear portion. A joint of this general type is disclosed, for example, in the Fraze U.S. Pat. No. 3,191,564.

In order to form a riveted joint of the requisite strength, and without destroying the continuity of the container wall, it has been found necessary to head the hollow rivet by extruding the material of the transverse end wall between cooperating die surfaces, with little or no axial shortening of the rivet, to form a bead clampingly engaged with the tab. During recent years, the rivets have become smaller in diameter and the aluminum alloys from which the easy opening container wall is constructed have become harder. These two factors have required relatively high compression forces to produce the extrusion of the transverse end wall to ensure an effective jointure but at the same time increase the danger of producing fissures or small cracks in the rivet during the staking operation.

In some containers, a sealant coating is applied to the inner surfaces of metal containers to keep the product within the container frommaking contact with the bare metal. Such a sealant coating is not only tenaciously adherent to the metal, but is also sufficiently ductile to survive the usual forming operations that are required to form the rivet integral with container wall. One problem ensuing from the extrusion of the transverse end wall is that the sealant coating applied to the interior surface of the container wall is fractured or destroyed during the extrusion operation because of the high compression forces required to produce the extrusion of the metal.

One reason for the sealant coating rupturing inside the hollow rivet in the course of the extrusion operation is the high unit stress involved in squeezing such a small area of the sheet metal. Another reason for the failure of the sealant coating is that prior to the extrusion operation, the sealant coating is weakened to some degree by the flow of metal involved in the initial formation of the hollow rivet. In any event, extrusion of the transverse end wall may rupture the sealant coating to expose the bare metal to the acid action of the product held by the container with consequent deterioration effect on the product.

SUMMARY OF THE INVENTION In early prior art joints, the only part of the tab which engaged the head of rivet was the rim of the aperture in the tab. The region of engagement was thus substantially in the form ofa line which surrounds the rivet. As

the bearing area between the rivet and the tab was minimal, the stress on the tab and rivet was high when the tab was manipulated to initiate severance of the tear portion. Such high stresses at times deformed the aperture and, in addition, the rim of the aperture presented a sharp edge to the bead or head of the rivet which increased the likelihood of rivet failure.

To lessen the likelihood of tab failure during the manipulation of the tab, it was proposed to form a right-angled hub about the defining rim of the aperture to increase the strength of the jointure. The hub reinforced the aperture and lessened the likelihood of the aperture deforming as the tab was lifted to rupture the tear strip. This prior proposal did not, however,solve all the problems inherent in the severe stressing of the tab in the region of the aperture. Of more importance, the hub in no way obviated the thinning of the sealant coating as the jointure still required the extrusion or cold flow of metal in the transverse wall of the rivet to form the bead or head clampingly mounting the tab to the container wall.

To solve this problem, the present invention teaches forming of the sheet material around the aperture of the tab into a smoothly curved frusto-conical boss having an annular, conical seat which circumscribes the aperture. The boss is formed with a generous radius at the base and substantially reinforces the aperture of the tab against deformation, as the boss is formed with a relatively larger radius there is no extreme deformation of the metal of the defining edge of the aperture as in the previously proposed bosses which extended perpendicular to the tab.

Furthermore, as the boss of the present invention presents the inwardly directed conical seat, the rivet used to form the jointure need not be as high as in the prior proposal where the right-angled boss presented a flat seat spaced farther from the container wall than the conical seat of the present invention.

As the rivet may thus be shorter in height than the rivets of prior use less deformation of the sealant coating occurs during the rivet-forming operation as less deformation of the container wall is required to form the shorter rivet.

In the process of completing the jointure of the present invention, a rivet is formed integral with the container wall by any of the processes heretofore developed; although preferable, a process should be used which does not involve a large amount of coining of the metal of the wall eircumscribing the base of the rivet. Coining requires high concentration of compressive stresses which, if excessive, can thin or fracture the sealant coating in the segment of the wall coined during the rivet forming operation.

As the rivet used to form the jointure need not have the height of rivets used in prior jointures, as will hereinafter be more fully explained, coining may be kept to a minimum with the advantage above-mentioned.

The tab is completed with conventional work operations which include the formation of an under-sized aperture, after which a suitable forming tool is used to form the frusto-conical boss which results in the annular conical seat. The tab is superimposed on the container wall with the rivet extending through the aperture, after which the rivet, with the upstanding or peripheral wall supported against inward collapse, is subject to a compressive force sufficient to cause the free end thereof to enlarge to form a bead or head forced into engagement with conical seat to conform to the contour of the seat.

Although the rivet is axially shortened, the axial shortening is not severe and an effective bead or head can be formed without severe bending of the upstanding wall. This obviates the formation of possible fissures which would prevent use of the wall as a closure for containers which must be hermetically sealed. As the bearing surface formed by the conical seat, and against which the head of the rivet is forcibly engaged, is relatively large and presents no sharp edges to produce high stress loading on the bead or head, a relatively strong jointure is formed even though the head of the rivet is no larger in diameter than the maximum diameter of the seat.

In the now preferred practice of the present invention, the included angle between the wall of the boss and the tab contiguous thereto is on the order of 45. When the initial aperture formed in the tab is produced by a punching operation, the conical seat resulting from the formation of the boss is also on the order of 45 to the axis of the boss.

This angular relationship results in a further important advantage in that the stresses created by the lifting of the tab produces little or no bending loads at the defining edge of the aperture in the tab. This is so for as the tab is lifted to initiate rupture of the tear strip, a segment of the boss forms a thrust element to apply a lifting force to the one side of the head of the rivet and the resulting reaction force is taken largely in compression by the short wall segment of the boss.

The invention may best be understood by reference to the following description taken in connection with the accompanying illustrative drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a can end constructed in accordance with the teachings of the present invention;

FIG. 2 is a greatly enlarged sectional view showing the unheaded hollow rivet extending through the aperture of the tab prior to the heading operation and also showing tooling that may be employed to carry out the rivet heading operation;

FIG. 3 is a view similar to FIG. 2 at the completion of the rivet heading operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing and in particular to FIG. 1 thereof, reference numeral 11 designates an easy opening container wall constructed in accordance with the teachings of this invention. The easy opening container wall 11 includes a can end 13 having a peripheral attaching flange 15 for attaching the can end to a can body (not shown). The can end 13 is constructed of a suitable aluminum alloy and may be formed with a concentric strengthening rib 17. In the illustrated embodiment of the present invention, a line of weakness in the form of a scoreline 19 defines a tear portion 21 which extends from a central location on the can end 13 radially outwardly toward the attaching flange 15. It should be understood that the shape and configuration of the tear portion 21 will vary, depending upon the intended use of the container. A tab 23 is attached to the leading end of the tear portion 21 by a hollow rivet 25 formed integral with the metal of the tear-strip. Although the tab 23 may be of any suitable design, in the embodiment illustrated it has a ring portion 27 for ease of manipulation of the tab.

By grasping of the ring portion 27 and exerting an upward pulling force, a force is transmitted through the rivet 25 to the leading end 29 of the tear portion 21 to cause rupture of thescoreline at that location. By exerting an outward pulling force, the scoreline 19 can be completely severed to completely remove the tear portion 21 to provide a pouring opening in the can end 13. Although the easy opening container wall 11 has been described with particularity, it should be understood that the present invention can be utilized with easy opening can ends and closures of many different configurations.

In FIG. 2 a hollow rivet 25 has been formed integrally with the sheet material of the can end 13 with any suitable process which may include coining of an annular region of the can end immediately surrounding the rivet 25. The rivet 25 has a transverse end wall 31, a peripheral wall 33, and a base 35 joining the rivet to a surrounding region 37 of the can end 13. The base 35 preferably should be formed with a radius such as to form a relatively strong fillet joining the wall 33 and the region 37 circumscribing the rivet. As shown in FIG. 2, the surrounding region 37 is of lesser thickness than the zone of the can end 13 radially outwardly thereof and this is the result of slight coining of the surrounding region 37 during the formation of the hollow rivet 25. The interior surfaces of the container wall 13 and of the hollow rivet 35 are coated with a sealant coating 39 of a material suitable for the intended product to be packed within the container to be closed by the wall 13.

The tab 23 is constructed of suitable sheet material, such as aluminum alloy, and is formed at the one end with an aperture 41. The aperture 41 is defined, in part, by a low profile, sloping, annular boss 43 which is formed by turning outwardly the region of the sheet material immediately surrounding the aperture 41. The boss 43 forms an angle of substantially 45 with a surrounding zone 45 of the tab 23 and in the embodiment illustrated is generally frusto-conical. The boss 43 terminates outwardly in a conical end face or seat 47. The seat 47 slopes downwardly, i.e., toward the can end 13 as it extends radially inwardly. In cross section, the seat 47 preferably forms an angle of approximately 45 with the axis of the boss 43.

In construction of the tab 23, the aperture 41 is punched or otherwise formed in the tab. Next, the region of sheet material immediately surrounding the aperture is bent out of the plane of the surrounding zone 45 through an angle on the order of 45 to form the boss 43. Preferably the radius of the boss 43 is quite generous and is complementary to the radius of the base 35 of the rivet 25.

To complete the jointure of the tab 23 and the wall 13, the heading of the rivet 25 can be carried out between a tool 49 and a punch 51. The tool 49 has a head 53 which is sized to fit within the hollow rivet 25 to support the peripheral wall 33 against inward collapse. The head 53 has an end surface 55 which is spaced substantially from the transverse end wall 31 when the head 53 is fully inserted into the hollow rivet 25. In the illustrated embodiment of the present invention, the punch 51 has a flat working surface 57.

By relatively advancing the tool 49 and the punch 51, the working surface 57 of the punch engages the transverse end wall 31 0f the rivet 25 to axially collapse and radially expand the outer end of the rivet 25 to form the head 59, as shown in FIG. 3. This heading operation is carried out without squeezing of the transverse end wall 31 between the end surface 55 and the working surface 57 of the punch 51. Accordingly, as there is no extrusion of the metal of the wall 31, the sealant coating 39 is not subject to stress inherent in the former practices and is not damaged during the heading operation.

As the outer end of the rivet is radially expanded to form the head 59, an annular segment 61 of the head is forced into engagement with the seat 47. In fact, the seat 47 shapes and contours the segment 61 so that the surface thereof engaging the seat has a slope complementary to the seat 47. The area of engagement between the head 59 and the seat 47 is substantial and the resulting jointure is relatively stronger than those jointures of prior developments when a right-angled hub was formed about the aperture of the tab.

When the tab 23 is lifted to apply a rupturing force to the leading end 29 of the tear portion 21, the seat 47 moves upwardly and applies a force to the circumscribing surface of the segment 61. Because of the relatively large area of engagement between the surface 61 and the seat 47, the head 59 of the rivet 25 is not locally stressed severely. Also, because the seat 47 and the surface 61 have complementary slopes, there are no sharp edges which might tend to apply high stresses at the point or points of engagement below such edges and the head of the rivet. The metal of the tab circumscribing the aperture is not overstressed as a result of the bending operation producing the boss and the latter reinforces the aperture against deformation as the tab is lifted. Because of the complementary shape of the seat 47 and the engaged surface of the segment 61, the upward lifting of the tab 23 tends to wedge the tab and rivet more tightly together and the forces acting on the boss 43 act generally in a direction to axially compress the boss. In other words, as the tab is lifted, the segment of the boss adjacent the lifting end of the tab forms a thrust element to apply a lifting force to the head of the rivet and resultant stresses are largely in compression because of the angular relationship to the frusto-conical wall of the boss and the segment 61 engaged by the seat 47.

Although the features of the present invention have been illustrated and described as embodied in an easy opening container wall, it should be understood that the invention is applicable generally to the interconnection of two or more members of sheet material.

Similarly, the invention is applicable to the use of riveted jointures generally in the easy opening container field.

Although a specific embodiment of the invention has been shown and described, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.

We claim: 1. The method of mounting a tab means on a can end of the easy opening type, comprising the steps of:

forming an integral hollow rivet having a transverse wall and a peripheral wall in said can end;

forming an aperture in a tab means;

forming a generally frusto-conical boss about said tab means aperture; placing said tab means aperture over said integral hollow rivet so that said boss terminates intermediate said transverse wall and said can end; and

radially collapsing said peripheral wall against the upper surface of said boss.

2. The method of claim 1, wherein said step of forming said boss further comprises the step of terminating said generally frusto-conical boss in a surface which is at an acute angle relative to the axis of said aperture.

3. The method of claim 1 wherein said step of forming said boss further comprises the step of terminating said generally frusto-conical boss in a frusto-conical end surface which slopes downwardly toward a plane containing said tab means as it extends radially inwardly.

4. The method of claim 1 wherein said step of radially collapsing said peripheral wall further includes the step of supporting a portion of said peripheral wall distal from said transverse wall against collapse.

5. The method of mounting a tab on a can end of the easy opening type, comprising the steps of:

forming a hollow rivet having a transverse wall and a peripheral wall integral with said can end; providing a tab for mounting to the can end;

forming an aperture in a tab;

forcing the material of said tab about said aperture out of the plane of the tab through an angle of approximately 45 to form a boss of a height less than the height of said rivet and having a frusto-conical end surface which slopes downwardly at an angle approximately 45 toward the plane of said tab as it extends radially inwardly;

mounting the tab to the can end with the rivet extending through the aperture of the tab to position said frusto-conical end surface intermediate said transverse wall and said can end; and

radially collapsing said peripheral wall against the frusto-conical end surface of said boss. 

1. The method of mounting a tab means on a can end of the easy opening type, comprising the steps of: forming an integral hollow rivet having a transverse wall and a peripheral wall in said can end; forming an aperture in a tab means; forming a generally frusto-conical boss about said tab means aperture; placing said tab means aperture over said integral hollow rivet so that said boss terminates intermediate said transverse wall and said can end; and radially collapsing said peripheral wall against the upper surface of said boss.
 2. The method of claim 1, wherein said step of forming said boss further comprises the step of terminating said generally frusto-conical boss in a surface which is at an acute angle relative to the axis of said aperture.
 3. The method of claim 1 wherein said step of forming said boss further comprises the step of terminating said generally frusto-conical boss in a frusto-conical end surface which slopes downwardly toward a plane containing said tab means as it extends radially inwardly.
 4. The method of claim 1 wherein said step of radially collapsing said peripheral wall further includes the step of supporting a portion of said peripheral wall distal from said transverse wall against collapse.
 5. The method of mounting a tab on a can end of the easy opening type, comprising the steps of: forming a hollow rivet having a transverse wall and a peripheral wall integral with said can end; providing a tab for mounting to the can end; forming an aperture in a tab; forcing the material of said tab about said aperture out of the plane of the tab through an angle of approximately 45* to form a boss of a height less than the height of said rivet and having a frusto-conical end surface which slopes downwardly at an angle approximately 45* toward the plane of said tab as it extends radially inwardly; mounting the tab to the can end with the rivet extending through the aperture of the tab to position said frusto-conical end surface intermediate said transverse wall and said can end; and radially collapsing said peripheral wall against the frusto-conical end surface of said boss. > 